Diesel engines may include a selective catalytic reduction (SCR) system in an emission control system to reduce emissions of nitrogen oxides (NOx) during engine operation. A reductant, such as diesel exhaust fluid (DEF), may be injected directly into an exhaust passage upstream of the SCR system through a specialized DEF injector in a DEF dosing system. In one example, the DEF is an aqueous urea solution. The injected urea solution mixes with exhaust gas and breaks down to provide ammonia (NH3) in the exhaust stream. The ammonia then reacts with NOx in the exhaust at a catalyst to produce nitrogen gas (N2) and water (H2O).
However, the urea of the DEF is susceptible to dehydration and crystallization. Hot exhaust gases may heat the DEF, causing water to evaporate and leave behind solid urea in the form of urea crystals. For example, a diesel particulate filter (DPF) regeneration event that is terminated by the end of a vehicle trip (e.g., a key-off event) may be a source of urea crystallization, as opening the DEF injector to purge the DEF dosing system at the end of the vehicle trip may draw in hot exhaust from the DPF regeneration event. The resulting urea crystals can clog the DEF injector and prevent DEF delivery to the exhaust passage. As a result of the DEF injector clogging, NOx emissions will not be reduced, and an emissions warning lamp may be activated.
Various strategies have been developed to address DEF injector clogging. One example approach shown by Cole et al. in U.S. 20140331645 A1 includes activating a remediation mode upon an indication of a clogged DEF injector. The remediation mode includes starting a timer and increasing the temperature of the exhaust gas in an attempt to melt urea crystals within the DEF injector. The DEF injector is then activated to evacuate any molten urea. Once a maximum remediation period has elapsed, a failure flag is set and the process is terminated.
However, the inventors herein have recognized potential issues with such systems. As one example, the method disclosed by Cole et al. is restricted to a finite duration once the clogged DEF injector is indicated. Depending on the vehicle operating status, it may not be possible to perform the remediation routine during that time period. Furthermore, raising the exhaust gas temperature may melt urea crystals within close proximity to or in direct contact with the exhaust gas flow but may not melt urea crystals that are not in close proximity to the exhaust gas. Thus, the DEF injector may remain clogged, the emissions warning lamp may remain activated, and additional repairs may be performed, increasing repair times and costs and increasing an amount of lost vehicle usage time.
In one example, the issues described above may be addressed by a method, comprising: while delivering diesel exhaust fluid (DEF) from a DEF dosing system to an exhaust passage of an engine via a DEF injector, indicating insufficient DEF injector flow in response to a duty cycle of a DEF pump being less than a first threshold duty cycle; and operating the engine in a DEF injector cleaning mode in response to the indication. In this way, the clogged DEF injector may be quickly cleaned without removing the injector from the vehicle.
As one example, operating the engine in the DEF injector cleaning mode includes operating the engine at a high idle speed, decreasing an amount of engine air intake flow (e.g., by decreasing an opening of an air intake throttle valve), and increasing an exhaust backpressure (e.g., by decreasing an opening of variable geometry turbine vanes). The engine may be operated in the DEF injector cleaning mode while servicing the vehicle, for example. Operating at the high idle speed with the decreased amount of intake air flow and the increased exhaust backpressure while servicing the vehicle warms the engine and enables the exhaust to reach normal operating temperatures (e.g., the temperatures reached when the vehicle is driven), thereby preventing SCR system degradation. By quickly cleaning the DEF injector while it remains in the vehicle, repair costs and loss of vehicle usage may be reduced compared with more time consuming cleaning procedures. As many diesel engines are used commercially (such as tractors used in interstate shipping), quick, cost-effective repairs may reduce company overhead.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.